The present invention relates to the art of nuclear medicine cameras. It finds particular application in conjunction with nuclear medicine cameras having an octagonal, more precisely a rectangular with clipped corners, radiation detector and will be described with particular reference thereto. However, it is to be appreciated that the present invention is applicable to nuclear and other types of scanning detectors with a non-rectangular detector shape.
Heretofore, nuclear medicine cameras have had detectors in a variety of shapes including generally circular, hexagonal, and octagonal. The octagonal detector was commonly a rectangular head with symmetrically clipped corners. When an image was taken with the detector held stationary, the resultant image was also a rectangle with symmetrically clipped corners. Because diagnostically significant information rarely appeared in the corners, a rectangular image with clipped corners was diagnostically satisfactory.
A problem arose, however, when the nuclear medicine camera was used in a scanning mode. In a whole body scan, for example, the detector was positioned over the upper portion of the patient. The detector was initially masked and then progressively unmasked starting at the transverse edge closest to the patient's head. When the detector was completely unmasked, the detector commenced moving longitudinally toward the patient's feet. At the end of the scanning movement, the detector head would stop and its face would be progressively masked starting at the edge toward the patient's head and moving toward the patient's feet.
As the detector moved longitudinally, the portion of the detector corresponding to each pixel of the resultant whole body image was indexed. In this manner, the value at each pixel of the resultant image was the integration or sum of a multiplicity of samplings with the detector at a corresponding multiplicity of positions. Note that for a pixel in a central portion of the image, i.e. corresponding to a region of the patient over which the widest part of the detector passed, the pixel value is the integration of values collected over the full width of the detector. By distinction, pixels near the transverse edges were the integration of values taken over a shorter length of the detector head due to the foreshortening attributable to the clipped corners. Thus, if the tissue corresponding to the pixel in the center were emitting radiation with the same number of counts per second as the pixel corresponding to the tissue at the edge, the number of radiation counts or events in the center would be higher. That is, the number of counts at the edge pixel was reduced by the degree of foreshortening caused by the clipped corners. Thus, the pixel values along the longitudinally extending edges corresponding to the clipped areas would be darker gray or more black. This graying of the longitudinal edges was not only cosmetically unattractive, but diagnostically misleading.
One solution to this graying of the longitudinal edges was to mask the detector. That is, the trapezoid at the longitudinal leading edge of the detector and the trapezoid at the trailing edge were masked, either mechanically or electronically. Once these two portions of the detector head were masked, the detector became effectively a rectangle of the same transverse width, but narrower in the longitudinal direction. This solution also had drawbacks. First, the effective longitudinal length of the detector head was now shorter. Hence, the detector needed to scan proportionately slower to collect the same density of information. The relatively expensive detector had the ability to gather significantly more data in the central region of primary interest but was prevented from doing so by the masking.
The present invention contemplates a new and improved nuclear medicine camera arrangement which overcomes the above-referenced problems and others.